(a) Field of the Invention PA1 (b) Description of the Prior Art PA1 (1) a preparation step comprising reacting phenol with formaldehyde in the presence of an acid catalyst and removing the acid catalyst, water and the unreacted phenol from the resulting reaction product to give a crude bisphenol F; and PA1 (2) a distillation step comprising distilling the crude bisphenol F to give highly pure bisphenol F, as a distillate, having a binuclear moiety-content of not less than 95% by weight, preferably not less than 98% by weight and a novolak phenol resin, as a still-bottom product, having a binuclear moiety-content of not more than 15% by area, preferably not more than 10% by area. PA1 (1) a preparation step comprising reacting phenol with formaldehyde in the presence of an acid catalyst and removing the acid catalyst, water and the unreacted phenol from the resulting reaction product to give a crude bisphenol F; PA1 (2) a distillation step comprising distilling a part of the crude bisphenol F to give highly pure bisphenol F, as a distillate, having a binuclear moiety-content of not less than 95% by weight, preferably not less than 98% by weight and a novolak phenol resin, as a still-bottom product, having a binuclear moiety-content of not more than 15% by area, preferably not more than 10% by area; and PA1 (3) a step of admixing the highly pure bisphenol F with the remaining crude bisphenol F to give bisphenol F for general use. PA1 (1) a preparation step comprising reacting phenol with formaldehyde in the presence of an acid catalyst and removing the acid catalyst, water and the unreacted phenol from the resulting reaction product to give a crude bisphenol F; PA1 (2) a distillation step comprising distilling a part of the crude bisphenol F to give highly pure bisphenol F, as a distillate, having a binuclear moiety-content of not less than 95% by weight, preferably not less than 98% by weight and a novolak phenol resin, as a still-bottom product, having a binuclear moiety-content of not more than 15% by area, preferably not more than 10% by area; and PA1 (3) a step of mixing a part of the highly pure bisphenol F with the remaining crude bisphenol F to give bisphenol F for general use.
Recently, there has been desired the development of highly pure bisphenol F having a high binuclear moiety-content and bisphenol F for general use, such as starting materials for epoxy and polycarbonate resins. On the other hand, various kinds of novolak phenol resins have been used as resist materials, binders for producing molds, hardeners for epoxy resins or base resins for epoxy resins and recently, they have widely been used, in particular, in the field of electric and electronic materials.
The present invention relates to a method for simultaneously preparing bisphenol F and a novolak phenol resin and more specifically to a method for simultaneously preparing highly pure bisphenol F having a high binuclear moiety-content and/or bisphenol F for general use as well as a novolak phenol resin having a low binuclear moiety-content, but having high contents of trinuclear and tetranuclear moieties, in particular, trinuclear moieties and a high molecular weight novolak phenol resin having a low binuclear moiety-content and a high trinuclear moiety-content.
Both bisphenol F and novolak phenol resins are prepared from a stoichiometrically excess phenol to formaldehyde in the presence of an acid catalyst. These are different, from one another, in the reaction molar ratio of phenol to formaldehyde (hereinafter referred to as "P/F").
In general, bisphenol F is prepared at a P/F ranging from 20 to 50 and the reaction product comprises three kinds of binuclear moieties, i.e., 4,4'-dihydroxydiphenylmethane (hereinafter referred to as "4,4'-moiety"), 2,4'-dihydroxydiphenylmethane (hereinafter referred to as "2,4'-moiety") and 2,2'-dihydroxydiphenylmethane (hereinafter referred to as "2,2'-moiety") as well as 7 to 12% by weight of 3-nuclear (trinuclear) to 5-nuclear (pentanuclear) moieties (hereinafter also referred to as "polynuclear moieies") formed through polycondensation of phenol and formaldehyde.
It has been known that the polynuclear moieties greatly affect the physical properties of an epoxy resin obtained through epoxidation of bisphenol F. This means that the resulting epoxy resin is liable to cause crystallization as the content of the polynuclear moieties decreases, while if the content thereof increases, the viscosity of the epoxy resin becomes high and this impairs the workability thereof.
First of all, bisphenol F for general use will hereinafter be explained in detail.
Bisphenol F for general use is a bisphenol F which comprises binuclear moieties in an amount ranging from about 88 to 93% by weight and preferably about 90 to 93% by weight and has effectively been used as a starting material for epoxy resins having a low viscosity.
Japanese Unexamined Patent Publication (hereinafter referred to as "J. P. KOKAI") No. Sho 55-124730 discloses a method for preparing bisphenol F for general use. According to this method, bisphenol F useful as a starting material for epoxy resins can be obtained by limiting the reaction molar ratio (P/F) of phenol to formaldehyde to the range of from 25 to 50.
In addition, J. P. KOKAI No. Sho 63-238032 discloses that the use of activated china clay as a catalyst permits the production of bisphenol F suitable as a starting material for epoxy resins even if the foregoing reaction molar ratio is reduced to a level of the order of 20.
In this method, however, the rate of bisphenol F produced with respect to the reaction mass is low in the order of about 0.1 although the reaction molar ratio (P/F) is about 20. This results in the reduction of production efficiency and requires a great deal of energy for the separation of the excess phenol.
Now highly pure bisphenol F will be explained below.
Highly pure bisphenol F is a bisphenol F whose binuclear moiety-content is greater than that of the bisphenol F for general use and is effectively used as a starting material for preparing epoxy resins for paint and varnish.
J. P. KOKAI No. Hei 2-166114 discloses that paint and varnish which comprise an epoxy resin prepared from a bisphenol F having a binuclear moiety-content of not less than 95% by weight, preferably not less than 98% by weight are excellent in, for instance, corrosion resistance and the resistance to chemicals of the resulting films is high compared with those achieved by paint and varnish which comprise an epoxy resin prepared from a bisphenol F having a binuclear moiety-content of 92% by weight.
However, it has been impossible for any conventional technique to prepare highly pure bisphenol F having a binuclear moiety-content of not less than 98% by weight through the reaction of phenol and formaldehyde even if the reaction molar ratio, P/F, is increased up to 100 or higher. In other words, the formation of such highly pure bisphenol F is industrially impracticable.
For instance, when a continuous equilibrium flash distillation is carried out after removing the unreacted phenol from the reaction product obtained through the reaction of phenol and formaldehyde, it is necessary, on the basis of the gas-liquid equilibrium, to control the binuclear moiety-content in a still-bottom product to not less than 30% by weight in order to obtain a distillate having a binuclear moiety-content of not less than 98% by weight. In such a method, however, a large amount of useful binuclear moieties remain in the still-bottom product and this makes the method less economical.
Japanese Examined Patent Publication (hereinafter referred to as "J. P. KOKOKU") No. Sho 39-8399 discloses a method for preparing highly pure bisphenol F. The object of this invention is to obtain a reaction product as a mixture of isomers thereof whose content of 4,4'-moiety falls within the range of from 40 to 80% by weight. This method comprises the steps of subjecting a reaction product to batch-wise simple distillation over two times to give a mixture mainly comprising binuclear moieties and then recrystallizing the mixture from toluene to give highly pure bisphenol F. However, this invention does not disclose the composition of the still-bottom product remaining in the still after the batch-wise simple distillation performed twice, the contents of useful binuclear moieties and polynuclear moieties included in the filtrate obtained after the recrystallization and methods for recovering the same. Moreover, the recovery of the useful components from the filtrate obtained after the recrystallization requires evaporation of a large amount of solvents used and hence a great deal of energy.
Novolak phenol resins will now be explained below.
A novolak phenol resin is a resin generally prepared through a reaction of phenol and formaldehyde at a P/F of 1 to 2 and having an average number of nuclear moieties of 4 to 5 and a binuclear moiety-content of 10 to 30% by weight.
It has been known that the distribution of these moieties in a novolak phenol resin is determined by the molar ratio, P/F, of phenol to formaldehyde. For instance, the reaction of phenol and formaldehyde performed at a P/F of 2 can provide a novolak phenol resin which comprises about 25% by area of binuclear moieties, about 20% by area of trinuclear moieties and about 15% by area of tetranuclear moieties. The higher the P/F ratio, the greater the binuclear moiety-content and the lower the softening point of the resulting resin.
The term "% by area" used herein for expressing the content of each moiety present in novolak phenol resins and high molecular weight novolak phenol resins is determined by subjecting these resins to gel permeation chromatography (using two columns, G4000HXL+G2500HXL+G2000HXL, available from Tosoh Corporation; eluent: tetrahydrofuran).
When the novolak phenol resin is used as a starting material or a hardener for epoxy resins, inconveniences such as the formation of flashes on molded articles and/or reduction of strength due to a decrease in the degree of crosslinking occur. For this reason, there has been desired for the development of a novolak phenol resin having a low binuclear moiety-content.
Moreover, it has also been desired for the development of a technique for reducing the contents of unreacted starting materials which do not contribute to crosslinking reactions and those of binuclear or lower moieties present in novolak phenol resins for improving the strength of the cured product when it is used as a hardener or a base resin for epoxy resin.
On the other hand, one of the important properties required for phenol resins is low viscosity. If the viscosity of phenol resins can be lowered while maintaining other characteristic properties such as heat resistance and strength, the workability, reactivity, flow properties and impregnating properties thereof would be greatly improved. Moreover, this permits incorporation of fillers such as inorganic fillers into these resins depending on applications.
In case where the resins are used as binders for producing molds, the resins must have low contents of binuclear or lower moieties, i.e., binuclear moieties and unreacted starting materials included in the resins in order to reduce the amount of smuts possibly generated during molding operations.
Further it has likewise been required for phenolic hardeners for use in epoxy resins which are used for electric and electronic applications, whose demand has rapidly been increased recently, to have low viscosities and low contents of binuclear moieties.
In general, phenol and formaldehyde are reacted at a low P/F ratio ranging from 2 to 3 to give a low molecular weight resin, i.e., a low viscosity resin. However, such a low viscosity resin has high contents of binuclear or lower moieties which do not contribute to crosslinking reactions. Therefore, if such a low molecular weight resin is used as a hardener, the hardness of the cured product is impaired.
For instance, when the reaction is carried out at a P/F ratio of 5/2 to reduce the viscosity, the resulting resin has a low molecular weight and a low melt viscosity. However, the reaction product has high contents of binuclear or lower moieties which do not contribute to crosslinking reactions and this leads to formation of products, during hardening reaction, which have insufficient strength. Accordingly, if the binuclear moieties are further removed, the resulting resin comprises about 35% by area of trinuclear moieties and about 23% by area of tetranuclear moieties in addition to binuclear moieties whose amount has been reduced. This resin can provide hardened products having sufficient strength, but cannot achieve a sufficiently low viscosity since the binuclear moieties are removed to a substantially low level.
Thus, when the reaction is performed at a P/F ratio of, for instance, 5/4 so as to reduce the amount of binuclear moieties formed, the resulting novolak phenol resin comprises 9% by area of binuclear moieties, 8% by area of trinuclear moieties and 6% by area of tetranuclear moieties. In this case, the contents of binuclear moieties are reduced, while those of high molecular weight reaction products formed during the reaction increase. This leads to an increase of viscosity and accordingly becomes a cause of various problems such as reduction of workability, reactivity, flow properties and impregnating properties.
In order to reduce the content of binuclear moieties present in a novolak phenol resin according to the conventional methods, the ratio, P/F, is necessarily reduced, but this leads to increases of the softening point and viscosity of the resulting novolak resin and this leads to deterioration of the flow properties of the resin during molding.
Under such circumstances, there has recently been tried to further reduce the content of binuclear moieties by dehydrating an initial condensate formed through a reaction, removing phenol as a starting material and then removing binuclear moieties through an operation such as extraction, steam distillation or distillation under reduced pressure. In this case, the removal of the binuclear moieties results in the formation of a hardened product having a strength higher than that achieved by the resin having a high content of binuclear moieties, but the viscosity of the product is correspondingly increased.
There have been known methods for preparing novolak phenol resins having low content of binuclear moieties. For instance, J. P. KOHYO No. Sho 62-501780 discloses a method comprising extracting binuclear moieties with hot water after the reaction of phenol and formaldehyde and J. P. KOKAI No. Hei 2-60915 discloses a method which comprises adding a solvent slightly soluble in water and then adding a water-soluble alcohol and water to remove components having small numbers of nuclei.
However, these method do not disclose any effective use of the binuclear moieties thus removed at all. Consequently, about 20% by weight of binuclear moieties, on the basis of the novolak phenol resin, are discarded. Moreover, the recovery of the useful binuclear moieties according to these methods requires evaporation of a large quantity of water and solvents used and this in turn leads to the consumption of a great deal of energy.
As binders for producing molds, there have been known, for instance, J. P. KOKAI No. Sho 60-133017 which discloses those having low contents of binuclear moieties and those of hexanuclear or higher moieties. However, the viscosity of the resin is still too high.
J. P. KOKAI Nos. Sho 62-267314, Sho 62-275121 and Sho 62-277419 disclose resins whose contents of binuclear moieties are lowered, but the viscosity thereof is still too high.
J. P. KOKAI No. Hei 2-70721 discloses an epoxy resin composition comprising, as a hardener, a novolak phenol resin whose binuclear moiety-content is not less than 1.0% by weight and not more than 5.0% by weight, whose softening point is not less than 80.degree. C. and not more than 120.degree. C. and whose number-average molecular weight is not less than 300 and not more than 900. This patent discloses that the resin is in general prepared by reacting formaldehyde with phenol in a reaction molar ratio ranging from 1:1 to 1:2.5. More specifically, formaldehyde is reacted with phenol in an amount of 1 to 2.5 times the molar amount of formaldehyde, the unreacted phenol is removed from the reaction system and then the binuclear moiety-content thereof is reduced to thus give a desired resin having a high degree of crosslinking. However, the viscosity of the resulting resin is too high to increase the amount of a filler to be added for reducing the linear expansion coefficient of the resin.
J. P. KOKAI No. Hei 3-24115 discloses an epoxy resin composition comprising, as a hardener for an epoxy resin, a novolak phenol resin whose binuclear moiety-content is not less than 20% by weight and whose content of the sum of binuclear and trinuclear moieties is not less than 35% by weight. The novolak phenol resin is a low molecular weight hardener and correspondingly has a low viscosity. Thus, the hardener permits an increase in the amount of a filler to be added such as an inorganic filler and in turn reduction of the linear expansion coefficient of the resin. However, the resin having a high content of binuclear moieties does not permit the improvement of the heat resistance of the resulting cured product and the high contant of volatile matter thereof does not permit any reduction of the rate of crack-formation.
J. P. KOKAI No. Hei 4-68020 discloses an epoxy resin composition comprising a liquid epoxy resin as an epoxy resin component and, as a hardener, a novolak phenol resin whose content of trinuclear moieties is not less than 80% by weight and whose softening point is not higher than 85.degree. C. However, this patent does not discloses any method for preparing the novolak phenol resin and the components of the resin other than the trinuclear moieties.
J. P. KOKAI No. Sho 62-119220 discloses a method for preparing a polyhydroxy compound having a content of the sum of binuclear and lower moieties of not more than 5% by weight and a content of trinuclear moieties of not less than 30% by weight. This patent discloses that the polyhydroxy compound can be prepared by reacting a dimethylol derivative of a substituted phenol as a starting material with phenol in the presence of a basic catalyst and then neutralizing the reaction product with an acid.
Therefore, the use of the conventional reaction molar ratio has never permitted the production of any novolak phenol resin having a low melt viscosity while maintaining the reliability of other desired characteristic properties such as mechanical strength and heat resistance, even if the contents of binuclear moieties is reduced.